Control circuits



April 4, 1950 F. D. SNYDER 23,217

CONTROL CIRCUITS Original Filed Sept. 7, 1944 Z 3 Z I E 3 I/// I 3 nsulaziorz 3 '1 \3/ 15 OfflFIIaf Insulation I I I 8- 32 0 710 17 I Off E95. 9 10 a INVENTOR n g Frederiakfl Snyder". 6-,.- M M 37 40 F 25;. T

33 ATTORN EY Reissued Apr. 4, 1950 CONTROL CIRCUITS Frederick D. Snyder, Milton, Mass., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Original No. 2,445,459, dated July 20, 1948, Serial No. 553,034, September 7, 1944. Application for reissue July 21, 1949, Serial No. 106,080

6 Claims.

Matter enclosed in heavy brackets appears in the original patent but forms no part of this reissue specification; matter printed in italics indicates the additions made by reissue My invention relates to electromagnetic apparatus which embody a holding magnet, and

more particularly to electric control circuits for magnetizing and demagnetizing the holding magnets of chucks or retentive relays and the like magnetic devices.

Electromagnetic chucks, as used on machine tools, have a holding magnet inductively associated with magnetizing coils which, when energized, induce sufiicient magnetism to firmly attach a magnetizable workpiece to the pole surface of the chuck as long as the energizing current continues to flow. Upon interruption of this current, the residual magnetism of magnet and workpiece is apt to maintain a magnetic flux strong enough to prevent taking the workpiece off the chuck. Therefore, a pole-changing demagnetizing switch is usually provided so that the operator, by quick and expert maneuvering, is able to put just enough reverse power into the chuck to cancel the residual flux. This requires appreciable skill as the demagnetizing switch must be teased back and forth until the operator strikes a point where the magnetic circuit is approximately fully demagnetized. Similar conditions exist with pickup and hoisting magnets as used on cranes.

It is an object of my invention to provide control means for electromagnetic chucks and the like magnetically retentive holding magnets which facilitate demagnetizing the retentive circuit and eliminate trial and error methods of the above-mentioned kind so that no particular skill is necessary for releasing the magnetic grip.

In electromagnetic contactors for electric con- 2 trol circuits, the retentive induction (remanence) of a magnetic circuit, formed by a stationary fieldpiece and a movable armature, has been utilized for holding the contactor in picked-up condition once the fieldpiece has been magnetized by a temporary electric current excitation. A direct-current of reverse polarity or an alternating current of low amplitude is usually applied in order to release the contactor by reducing the attractive force of its residual magnetism below that required for overcoming the opening tendency of the armature bias. Referring to such contactors, it is also an object of my invention to provide simple and reliable demagnetizing or release means; and it is a further object relating to such contactors to devise demagnetizing circuits that permit obtaining a desired timing or delay of the release performance.

In order to achieve these objects, and in ac,- cordance with my invention, I provide an electric holding magnet of the type referred to with a capacitor which is charged previous to the release operation and which is caused to pass a demagnetizing discharge through the magnet coils for canceling or reducing the residual magnetism of the holding magnet. The capacitor and coil circuit is so rated as to produce a demagnetizing efiect suficient to eliminate the residual flux in one or a few successive discharge operations.

According to another feature of the invention the control circuit of a holding magnet is equipped with a control switch whose operation, when releasing the magnet, causes a capacitor to be charged and discharged twice or several times so that the integral effect of the several discharges results in the desired demagnetization. According to still another feature, related to the one just mentioned, each subsequent charge imposed on the capacitor is caused to flow through the magnetizing coils of the holding magnet in the direction opposite to the original magnetizing current so as to contribute also to reducing the residual induction.

In still another aspect of my invention, I provide charging means for the above-mentioned capacitor which include a potentiometric circuit so as to permit a desired adjustment of the charging voltage of the capacitor or a change of this voltage in accordance with the particular requirements of each case of application.

In conjunction with any of the features mentioned in the foregoing and in accordance with a further essential point of the invention, the capacitor for issuing a demagnetizing current is so rated relative to the coils of the magnet that it forms an oscillatory system therewith with the effect of producing an alternating discharge current of a substantially given frequency and attenuation.

Lastly, it is also a feature of the invention to apply a capacitor discharge, in the manner referred to in the foregoing, to an electromagnetic contactor of the retentive type so that demagnetization of the relay involves a rated or metered timing effect which imparts to the relay the characteristic of a timing device.

These objects and features of the invention will be apparent from the following description of the embodiments illustrated in the drawing in which:

Figure 1 shows a top view of part of a holding magnet appertaining to an electromagnetic chuck, the coils of the magnet being omitted in this illustration;

Fig. 2 is a diagrammatic showing of a section through the holding magnet shown in Fig. l and indicates also the appertaining coils;

Fig. dis a controrcircuit according to the inventionionoperating a-holdini'g magnet as shown in Figs. 1 and 2;

Fig. 4 shows diagrammatically another embodie ment of a control circuit for chucks;

Fig. 5 is a similar circuit diagram representing variety of available chucks. The chuck, as shown,

is intended for a machine tool in whichthe body I "oftthe 'ma'gn'etis mounted on "a' reciprocating machine portion for carryingaworkpiece along a stationary tool. "Howeverpa'similarichuck may "also be used as astationary machine partffor holding a workpiece "relative to a mo'vabl'e to'ol; and it will also be understood'that theprinciples of my invention are likewiseapplicable to chucks of the rot'ating'type"such'asusedon l'ath'e's. The "body I "of theholding magnet is provided with spaced projections 2 forming between them a series'of grooves Thegrooves 3 are provided 'with coils denoted by 4f'and5. Thesepoilsare "all connect'ed'witho'ne another and so wound "that the projections? form alternating'north: and

'N and"S, respectively. The top surfaces of the projections '2 form the "supporting surface for -the workpiece B of 'm'agnetizable 'material. 'Whenthechuok windingsare"energized, the magnetic "flux issuing from each "north-pole to "the adjacent south poles passes "through the :workpiece 3 and *p'r'oduces"'su'fficientattraction to hold the workpiece firmly against "the chuck. This holding force obtains as 'l'o'nga's'theeriergizing direct currentpasses through th'e"coils. Upon 'interruption'of thecurrentfthe attractive force is reduced. However, the re'manent magnetic induction of theholdin'g magnet IQOro'i the Workhiece'B; or both, "remains, as arule, suffi'cientto prevent lifting "the workpiece from *the chuck. Hence, it is necessary to-apply a demagnetizing force'to the magnet. This-isalsddesiredin cases "where the'ipersist'ence' of an appreciable 'r'emanen't magnetism 'intheworkpie'ce B'after its removal fromtl'ie-"chuck is undesirable.

The control circuit of'coils l and Eisschemati'cally shown in Fig. 3. In'this figure, the totality of coils is represented "schematically 'by a single winding W. This windingis'connectedto directcurrent terminals 6 and I through a single-pole "on-"a'nd off'conta'ct. A "capacitor. C is connected across the Winding 'TW. "This capacitor 'C is so rated relative to "the winding 'Withat "a charge impressed son the capacitor b 't'he line voltage suificesto store sufiicient energy'for demagnetizing the winding. When-swit'ch 8 is closed'the winding W is energized-and induces in the chuck the magnetism necessary "forffirml-y attaching the workpiece. Switch "8 remains closed as long as the chuck is in operation. 'During'the closure of switch 8, the capacitor C collects a charge. When the switch aisopened-thereby interrupting "the magnetizing current, the capacitorv discharges itself through winding W. The discharge may occur as represented by the voltage-time curve in Fig. 6. As long as switch 8 is closed the voltage across-the capacitor C is at' its maximum value E.

At the moment of interruption, denoted by TI 5 in Fig. 6, the capacitor begins issuing its charge athrough winding W. The winding and capacitor form an oscillatory system so that the discharge "currentis alternating. Due to the fact that the magnitude of this current declines gradually, the alternating 'magnetizing force imposed on the magnetic-circuithas the effect of reducing the magnetic remanence. Hence, upon cessation of the"dischargeflth'eworkpiece can be lifted from 'the chuck.

A control circuit as described in the foregoing is siihicient for smaller chucks. In order to obtain a sufiicient demagnetization also in case of larger chucks rand workpie'ces without requiring capacitors of extremely large rating, a repeateddem'agnetizing performance is preferably provided for. To this end, the control circuit may be designed .as representedin Fig. 4. According to Fig. 4, the Win'din'gWV and the capacitor C are connected 'to direct-current supply leads "'9 "and it through 5 a multieposition -control switch S. In th'eer'nbo'diment of Fig. 4, thiscontrol switch S is-of the rotary type and has four positions. Inorderfizo facilitate explaining a'full cycle of' operation of the switch, its con.tact"elem'ents"are illustrated in developed form, an'don-eofits 'four' posit-ions, i. e.

the on position, is "shown't'wi'ce. "The-control which is rotated by means of a shaft 'l '2 andan 'op'erator a'ctuable handle [3. Amumberof s'ta- 7 h tionary"contact 'fingers, "such 'as those denoted southpoles'asis indicatedin '2'by the letters by M, co-operate with contact segments f5 "through 'ltwhi ch aremount'ed on the rotatable body I I. 'The direction "of motion is indicated by thearrow'marked A. 'A rheostat'is denoted 40 irR.

- In theillustrated off position of the switch, th'e'Winding W is short=circuitedbythe capacitor C and disconnected fromthe leads 9 and lll' of I a "dire'ctcurren't line. The 'chuc'k'isnow in condi- "tion'to receive a workpiece. Upon placingthe workpiece on the-chuckyswitch s is turnedto position I. In"this position leadfl is connected through segment I5 with one terminal of winding W, while theother terminal of the winding is connected through segment T1 with lead H).

Consequently the chuck coils are now energized chuck. The capacitor Cremains'connected' across winding Wby segment H and hence is charged.

'In'or'der to release the-workpiece,'the switch S is turned into'position II. Thishasthe-effect of disconnecting winding W-irom both leads 9 and -10, while "the capacitor "C remains connected across the winding. a 'result,'-the-'capacitor .passes a demagnetizingdischarge current through thewinding in the manner described "above. Upon continuance of its rotation, switch'S passes through its -position "III. In this position, the "left-hand terminal "of "winding W remains dis- ,65 'jconnecte'dso'that the winding stays de-energize'd.

The capacitor "0, however, is now connected "at one "ofits terminals to lead lll'thr'ough segment "I6. The'oth'erterminal of "the capacitor is con- "ne'cted'thr'ough segment 1'8 "to the slider of rheo- .70 j's'ta'tR. Attlie same'timejthe'resistor of rheostat R. is connected through segment I i! across'leads 9 and Ill. Consequently, the capacitor C is now charged from the line undera voltagedet'e'rrnine'd by the setting of therheostat, a'iid'this voltage .15 of opposite polarity as compared with *that cam? previously effective across the capacitor, and the Voltage is so chosen by correspondingly positioning the rheostat slider that the subsequent discharge suifices to demagnetiz-e the chuck to the extent needed for permitting the removal of the workpiece.

In the last position of switch 8, which is identical with the off position, the capacitor C is again connected across winding W and both are disconnected from the line.

The embodiment shown in Fig. involves a further improvement over that of Fig, 4., The control circuit of winding W and capacitor C includes a rheostat R and a control switch S, as in the embodiment of Fig. 4. The switch S has its rotor 2| provided with seven segments denoted by numerals 25 through 3| for co-operation with stationary contact fingers such as those denoted by 24. The switch has four contact positions of which the ofi position is shown twice in the developed diagram. In the off position, winding W and capacitor C are connected in parallel through segments 21 and 30 and are both disconnected from the line. In position I, lead I0 is connected through segment 25 with one terminal of winding W, while the other terminal or" the winding is connected through segment 21 with lead 9. The capacitor remains in parallel to winding W. Hence the chuck is now magnetized and the capacitor charged. In position II of the switch, winding W is disconnected from the line so that the capacitor passes a discharge current through the winding as in the previous embodiments. In the third position, lead 9 is connected through segment 26 to one end of winding W, while the other end of the winding is connected through segment 29 with one pole of the capacitor C. The other pole of the capacitor is connected through segment 28 with the slider of rheostat R. The rheostat R is connected across the line through segment 3!. Consequently, in this third position, the capaci tor is charged in accordance with the voltage setting of the rheostat R, but in contrast to the embodiment of Fig. 4, the recharging current passes also through the winding W. This current, however, is limited to the displacement current of the capacitor and its direction of flowin winding W is opposite to that of the original demagnetizing current. As a result, the recharging current of capacitor C performs also a demagnetizing effect. In the last position of switch S which is identical with the initial off position, the capacitor is again discharged through winding W. It will be noted, however, that this second discharge has a polarity opposite to the first discharge as typified by the voltage time curve F in Fig. 7. The discharge begins at the moment T2, and its first and largest magnitude is in the demagnetizing direction of the holding magnet.

It will be apparent from the above described examples that the use of a capacitive discharge current for producing a demagnetizing effect according to the invention involves the application; of a metered or limited demagnetizing effect which secures a definite reduction in remanent magnetism each time it is applied to the magnet coils. Hence, the control means according to the invention eliminate the above-mentioned trial and error method, and permit obtaining a sufiicient demagnetization without requiring any skill or timing in the actuation of the control switch, repeating the capacitive charging and discharging operation if necessary. Chucks for machine tools designed in accordance with Figs. 4 and ,5;

are usually suflicient to produce Substantially total demagnetization by a single full-cycle operation of the control switch. Of course, if desired, the recharging and discharging steps corresponding to switch position .III'and oil may be repeated.

The embodiment of a magnetically retentive contactor shown in Fig. 8 serves to exemplify the use of the invention for obtaining a timing effect. According to Fig. 8, the magnetic circuit of a relay formed by a stationary fieldpiece 32 and a movable armature 33 contains magnetically retentive material so that the'armature 33 remains attracted and sealed against the fieldpiece 32 once the latter has been magnetized suflicient- 1y. The fieldpiece 32 is provided with a magnetizing coil 34 and a demagnetizing coil 35. Coil 34 is connected through an interlock contact 36 and a control contact 31 between the direct-current terminals 38 and 39 of the relay circuit. A contact 4!] permits connecting a capacitor C across the direct-current terminals in series with a current limiting resistor 4|.

- The armature 33 is provided with a main con-' tact assembly (not illustrated) to be controlled by the relay. The interlock contact 36, which may form part of the main assembly, is closed when the armature is in the open position, and is interrupted when the armature is attracted by the fieldpiece and has moved through most of its travel toward the fieldpiece. The two contacts 31 and 40 are interconnected so that the contact 40 shifts from one to its other stationary connections when contact 31 is closed and opened.

' In the condition shown in Fig. 8, the magnetic circuit of the relay is de-energized. When contact 31 is closed, coil 34 is energized so that sufficient magnetism is induced in fieldpiece 32 for attracting the armature 33. The armature moves upwardly and, near the end of its travel, interrupts the magnetizing circuit at contact 36. Although the energizing current is now interrupted, the armature 33 remains in picked-up position due to the residual magnetism of the magneticcircuit. At the same time, contact 40 connects capacitor C across terminals 38 and 39 so that the capacitor is charged through resistor M. In order to release the relay, contact 31 is opened. This causes contact 40 to connect the capacitor C across coil 35. As a result a discharge current passes through the coil and demagnetizes the magnetic circuit until the residual magnetism becomes lower than is necessary for overcoming the armature bias. The armature will then drop off so that the relay system is in its original condition and ready for a new operation.

The demagnetizing current flowing in the oscillatory system of coil 35 and capacitor C reduces the retentive induction of the magnetic:

circuit during each second half cycle of an alter-- nating magnetizing force occurring substantially in accordance with a curve of the type shown in. Fig. 6 or '7. The effect of this stepwise demagnetization is cumulative and hence requires the occurrence of a multitude of alternating cycles before the relay drops ofi. In other words, the demagnetizing effect is not instantaneous but extends over a period of time which depends on the rating of the capacitive charge and the frequency and attenuation of the discharge current. A change in any of these determinants permits changing and adjusting the timing period of the relay.

ifiempii'figdifhy the Emm embodiments dp56ribed in .LthB} foregoing and mill ;-be :understood by :those :skilled -in ithe..-art iupon finfitlidy jfroma direct-current source,;a capacitor, .asselec- .tive ;control switch .-movable between ;-at fleast .three sequential positions and having three respective sets of contact imperative when said switch is in said cIBSDEGti-VB :three spositions] means, a first. one ,of :said sets nf-[contactsabeing connected :to] contact means gconuccting vv:said

coil .means and; said 1 capacitor [and] parallel :to each other across said circuit means so as 1130 magnetize said magnet and charge said; capacitor .whemsaid switch is in one of I said -.positions .[to

Substantially .demagnetize the chuck .awhen csaid switch is in the anextxposition], a second one of said setsroficontacts] coutactmeunsconnecting said .coil means ,only across said capacitor for discharging said capacitor :through said coil means tocubstantially demagnetizexgthe chuck whengqsaidsswitch-is lin theuext position, and'athe thirdset;of [contacts; beinglconnectedatoi contact means connecting-said circuit means .iliand] rionly to said capacitor for recharging said capacitor [while maintaining said; coil rmcansvdisconnccted from said capacitor and-said circuitimeans when said switch is :in :the third position];

.12. -With .amagnetic .-chuck.;having la -:[holding magnet] magnetieable member, ithe combination of .coil means inductively associated 3 with said [mag-net] --membcr, :circuit zmeans rfor supplying energizing direct current :eto g-said coil means, a. capacitor, a control switch disposedzbetween-said coil means, capacitor-and icircuit ":means and having atrleastifoun sequential positions and ;f our sets of respective :[contacts] contact-mimics iof which only one setis lefiective :ats-a time .depending upon the positionaof ;,Said-1switch,:one of said sets of [contacts Lbeing connected to. .saidcircuit means and] contact means lconnecting said coil means and said .capacitor parallel to each other across said circuit means -;to -magnetize gsaid [magnet] member .and charge :saidrcapacitor when said switch .isin {the "first position eachzof the second and fourth setsloflcontacts]ycontact means being attached only ptowsaid coil .means and said capacitor and connecting said capaci. tor across said -coil means ifordischarging said capacitor ithrough asaid coil means :-to substan.\- tially demagnetizesthe 'chuck \when said ;sw-itoh is :in the. second :and fourth positions respective ly,-.and the thirdset :of' lfcontacts'lcoutact means connecting said .capacitor only :to --said circuit means for-rechargingsaid capacitor when-said switch is in the i'third position.

:3 "Witha I holding magnet; the combination of coil means inductively associated'with said -..magnet, circuit =-means .for supplying :encrgizingdirect current to said coil -means,-,a icapacitor wfor 2811b stantially demagnetizingzsaid magnet iby .discharging through :said coil .means, .a control switch having .atizlea-st :three positions and three respective sets of [contacts] icontoct. means of which only one set is effective at a time dependdug upon *the "position of said switch, a first one of said :sets of {contactsll contact means "conmeeting-said circuit \means EIEto] across said coil =means :and across said capacitor :to magnetize said -magnet andcharge said capacitorby -voltage of one polarity when said switch is in one position, a second one of said sets of [contacts ;.being.-connected only to] contact means-connect- ?ing said coil means [and]-across said capacitor for discharging said .capacitor through said coil means when said switch is in another position, and the third --set of '.[contacts] contact means :connecting said circuit -means only to said capacitor and having reversed polarity of connec- =-tion ascompared with saidfirstset {of contacts] solasto charge said capacitor by voltage of opposite olarity when said switch is in the third position.

=4."With.a magnetic chuck having a [holding magnet] magnetizable member, the combination of -:coil means inductively associated with said lllmagnet] membencircuit means =for energizing said coilmeans .from a direct-currentsource, a capacitor, a potentiometric rheostat, andcontrol means having a selector switch with at least threeselective positions, saidswitch having three sets of [contacts] contact meansof which only one-set is eifective'at a :timedepending upon thev position of said sWitch,-0ne of said sets-of [contacts] contact means connecting said -[circuit means to said] coil means and said capacitor parallel to each other across said circuit'means to --magnetize said [magnet] memberand charge said-capacitor when said switchis'inone of said positions, another one of said sets of-{contacts-jl contact means connecting said coil means across said capacitor for discharging said capacitor through said coil means whensa'id switch is in another position to substantially demagnetize said [magnet] member, and the third set of [contacts] contact means connectingsaid circuit means "to saidrheostat and said capacitor so as to recharge said capacitorthrough said rheostat when said switch is in the third position.

"5. Magnetic-chuck control means, comprising terminals for connection,to d chuck coil, direct- .current'supply means for energizing, said terminals, a capacitor, a selective control switch havingot "least three sequential positions and howingthree sets of contact means operative when said switch is in said respective three positions, a first one of said sets of contactmeans connect- .ingsaid-terminals and said capacitor in parallel relation across said current supply means so as to -cnergize said terminals and charge said capacitor from said supply means when said switch is in one ofsaid -p0sitions, a second one of said sets of contact means connecting said terminals only across said capacitor ,for discharging -said capacitor, and the third set of contact means connecting said supply means to said cw'pacz'tor or recharging said capacitor, at least one of said terminals being disconnected from said capacitorcnd from said supply means when said switch is in the third position.-

6. Magnetic-chuck control --means, comprising terminals for connection to'a chuck coil, directcurrent supply means for energizing said terminals, a capacitor, a control switch havingat least three positions and three respective sets of contact'means oi -which only one set is ejiccti1.- e at a time depending upon the position of said switch, a first oneiojsaid sets ofcontact means connecting said terminals and said capacitor in parallel relationocross said current supply means to energize said terminals and charge said capacitor by voltage of one polarity when said switch is in one position, a second one-,of said sets of contact means connecting said terminals only across said capacitorjor discharging said capacitor through said terminals when said switch is in another position, and the third set of contact means connecting said current supply means only to said capacitor and having reversed polarity of connection as compared with said first set of contact means so as to charge said capacitor by voltage of opposite polarity when said switch is in the third position.

FREDERICK D. SNYDER.

REFERENCES CITED The following references are of record in the file of this patent or the original patent:

UNITED STATES PATENTS 

